Heating control system



Feb. 9, 1954 K D|ETR|CH 2,668,701

HEATING CONTROL SYSTEM Filed Feb. 5, 1951 2 Sheets-Sheet l FlG.l

' INVENTOR.

KARL L. DIETRICH ATTORNEY.

1954 K. DlETRlCH 68,7

HEATING CONTROL SYSTEM Filed Feb. 5, 1951 2 Sheets-Sheet 2 FIG. 4

INVENTOR. KARL 1.. DIETRICH ATTORNEY.

Patented Feb. 9, 1954 HEATING CONTROL SYSTEM Karl L. Dietrich, Philadelphia, Pa., assignor to Selas Corporation of America, Philadelphia, Pa., a corporation of Pennsylvania Application February 3, 1951, Serial No. 209,272

16 Claims. 1

;The present invention relates to the continuous heating of strip material, and more particularly to apparatus for heating strip material to an accurately controlled predetermined temperature as it is passing from one piece of apparatus to the next during the processing thereof.

While the present invention can be used in the heating of any strip or strand material, it is particularly applicable to the heating of thin ferrous stock to be used for tin plate or to be galvanized or annealed, and will be so described. In the electrolytic tinning of strip material the strip is moved through a bath in which athin coating of tin is deposited on its surface. This coating, however, has a dull finish and is porous. In order to produce a bright finish that is necessary for the canning industry, for example, it

is necessary to heat the strip above the melting point of tin so that the tin will flow in a smooth shiny coat over the base strip. In annealing strip metal it is desirable to bring the strip up to annealing temperature as rapidly as possible, and preferably in a non-oxidizing atmosphere. If desired, the strip can be moved to a galvanizing bath directly after it has been annealed.

It is highly desirable to accomplish each of the above-mentioned heating applications as rapidly as possible. Therefore, the temperature of the furnace must be considerably higher than the temperature to which the strip is to be heated, and this temperature will depend upon the speed of the strip as Well as its thickness.

It is an object of the invention to provide means for heating continuously a strip of material to a predetermined and accurately controlled temperature. It is a further object of the invention to provide a pair of opposed heating panels between which a strip is moved continuously to be heated, and means to control the heat supplied by the panels to the strip.

It is a further, and more specific, object of the invention to provide means for controlling the supply of fuel to a strip heating furnace in response to both the speed of the strip passing through the furnace and the temperature of the strip as it leaves the furnace. It is a further specific object of the invention to provide means to control the supply of fuel to a strip heating furnace, comprising a pair of opposed radiant panels, in response to the speed of the strip, and in response to strip temperature to vary the spacing of the panels relative to the strip.

The furnace of the present invention comprises a pair of elongated and oppositely disposed panels that form a furnace chamber through which the strip passes, preferably in a vertical direction. Each of the panels is provided with a plurality of radiant type burners that are directed toward the strip to heat the same by radiant heat and hot products of combustion. Means is provided to control the supply of fuel to the burners in response to the speed of the strip. This meanscan be adjusted to compensate for strip of different gauge. Means is provided to supervise-the basic fuel control from strip speed by adjustments made in response to strip temperature.

These can either be applied directly to the fuel' tages and specific objects attained with its use,

reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

In the drawings:

Figure 1 is a section view showing the furnace used with the present invention;

Figure 2 is a view taken on line 2-2 of Figure 1;

Figure 3 is a view showing the control system used in accordance with the present invention; and

Figures 4 to 6 are views of modified forms of the control system according to the present invention.

Referring to Figure 1, there is shown a furnace comprising heating panels I and 2 which form a furnace chamber 3 through which the strip S to be heated is passed. The strip passes into the furnace from some point of supply over a guide roller 4 and vertically downward through the.

furnace. It is obvious, however, that the strip could be passed upwardly if it was so desired.

The panels forming the opposite sides of the furnace are duplicates so that a description of one will sufiice. Each panel is mounted on a frame 5 that is provided with wheels 6 so that the panels can be moved along rails 1 toward and from each other. Movements of the panels are obtained by a shaft 8 that is driven by a suitably powered electric motor 9. The shaft 8 is provided on its opposite ends with reversely In the latter case means is provided to are held in place in accordance with ordinary furnace practice; the remainder of the walls being formed of refractory material I 4. The refractory and the burners are backed up in-the usual manner by sheet metal work I5 that'can' be suitably braced with structural elements. It willbe seen from Figure 2 that the panel 2" isprovided atxits side with an extension I6 which overlaps the adjacent edge of panel I. provided with an extension I! that overlaps the adjacent edge of the panelv 2. These extensions are each provided with a seal I8 of asbestos: rope or. the like tobear against the side of the other panel in order to prevent infiltration of air into the furnace chamber. Thus it will be seen that the furnace panels may be moved toward and from each'other for an extent equal to the-length of the extensions Without opening the furnace chamber. away fromeach other may, of course, be obtained in order to provide access to the interior of the chamber or for threading the strip through the furnace when such is necessary.

The burners may be of any suitable type, but are shown hereinas being a radiant type burner of the kind disclosed in Hess Patent 2.2151179,

granted September 17, 1940. These burners each comprise a block of refractory material that is provided in its face with a depression I9. E'xtending through the burner from the outside thereof and into the depression is a distributor member 2| through which fuel comprising a combustible mixture of gas and a combustion'supporting gas is supplied; Each of the distributors is connected by a pipe 22 with a manifold 2301'24 depending'upon whether the burner is located'in panel I or 2. It is noted that each of the supply" pipes 22 is providedwith a manually adjustable valve 25. Burners of this type are supplied with fuel through the distributors ill from which the fuel issues in a plurality of radially directed jets to burn along the surface of the cup. I9 and to heat the same to incandescence. Radiant heat from the cups is directed against the sides of the strip to provide radiant heating therefor. In addition, heat is also obtained by convection from the hot products of combustion resulting from the burning of the fuel. In the ordinary operation of furnace panels of this type the fuel is supplied to the burners so that they are heated to incandescence. As the strip is moved between the panels the radiant heat from the burners is directed against the same. It. is noted from an inspection of Figures 1 and 2 that the burners are disposed in a plurality of superposed horizontal rows. Each row may have in it a sufiicient number of burners to extend across the Width of the. strip that is being heated. Preferably the burners are offset with respect to each other so that one row will have, for example, four burners while the next adjacent row will have three burners. The panel, on the opposite side of the strip will have three burners facing the. four burners and four burners facing the three burners etc. By arranging the burners in this particular fashion- Additional movement of the panels- Similarly the paneI' I is the strip will be heated evenly from edge to edge and there will not be dark streaks produced in the strip as would result if each of the burners was directly above and opposite each of the other burners. The heat supplied by the burners to the strip can be varied by regulating the amount of fuel that is supplied to the burners to vary the incandescenc to the cups. The temperature of the strip can also be regulated by moving the panels toward and from the strip since the amount of radiant heat absorbed varies appreciably with the distance of the object from the source of heat.

Referring to FigureB, it will be seen that the lower ends of manifolds 23 and 24 are connected to a supply pipe 26 having in it a control valve "21.. The valve is shown herein as being pneuspeed of the strip and by its temperatureas itleaves the furnace chamber. The inventioneomtemplates a control of the amount of fueisup plied to the burners in response'tothe sp'eedof the strip and an adjustment of this fuel in ac-= cordance with the temperature ofthe strip. The control system is shown in Figure 3 and will now be described.

Roller 4 over which the strip passes on its'wa y" to the furnace is driven by this strip and in turn; through a shaft 28, operates an'elec'tro-pneumaticrelay of any commercial type. As is shown, herein, the relay includes a' tachometer-generator 3% that is connected either'directly or through suitable gearing to the shaft 28. The output fromthis generator is impressed upon a coil 32 of a solenoid. The core 330i the solenoid actstomove a lever 35 around its pivot 36 against the forceof a suitable spring 31. serves to adjust'the output pressure of a pneumatic pilot valve 38'. For this purpose the rightend of lever 35 is connected to a stem 3 9"of the pilot valve whichstem has upon it an inlet valve 41 controlling the flow of air from a supply 42" under suitable pressure. The stem 39 also has on it an outlet valve 43 that controls the exhausting of air through a port from the pilot-valve. It'wili be seen that as the lever 35 is moved around its pivot in response to the action of the core 33 a greater'or smaller pressure will be applied by the pilot valve 38' to a transmission line 64. Thisline leads to a relay 45 which converts the pressure 44 into a pressure that is proportional thereto.

The relay 45 includes a chamber 46 to" which the pressure from pilot valve 38 is applied, whichchamber has a diaphragm 41- forming one wall thereof. Movement of the diaphragm 47 in re sponse to pressure changes in the chamber is transferred'toone end-of a lever-48 that is pivoted at $9. Action of the diaphragm is opposed"- by a spring 51 on the oppositesideof the lever:

Movement of the lever 48 around itspivot isused toactuate a pressure regulator. 52 whose operation is opposed by a spring 53. The. pressure regulator includes a chamber, one end of;

which is closed by a diaphragm 55- that is connected by a hollow post 55to the lever 48'. Air:

Movement of the levervalve 59 that is biased toward a valve seat formed in the diaphragm 55 by means of a spring It will be seen that if the lever 48 turns clockwise in the drawing that spring 6| will close valve 58 while the diaphragm moves away from the outlet valve 59, thus permitting air to exhaust through the hollow stem 56 to the atmosphere to reduce the pressure in chamber 52. On the other hand, if lever 48 moves in a counter-clockwise direction the lever will force the diaphragm against the exhaust valve 59 to close the exhaust port and will move valve 58 against the force of spring 6| in order to open the inlet to chamber 52 and thereby increase the pressure therein. When the pressure in chamber 52 is proportional to the pressure in chamber 46 in accordance with the ratio of the lever arms above and below the pivot 49, the relay will be in a static position. When the pressure in chamber 46 is varied due to a change in the speed of the strip the equilibrium conditions of relay 45 will be varied to produce a new output pressure proportional to the pressure in the chamber 46. This output pressure is applied through a line 62 to a relay 63 that is substantially similar to the relay 45. Pressure applied through line 52 acts in a chamber 11 to move the lever of relay 63 to thereby cause a pressure to be produced in output chamber 18, depending upon the position of movable fulcrum 55. The output pressure from chamber 18 is applied through a pipe 54 to the diaphragm of fuel control valve 21. It is noted that a single source of compressed air regulated to a suitable pressure may be used for the various components of the control system.

From the above description it will be seen that a change in the speed of the strip will cause a change in the pressure applied to the diaphragm of valve 21. This may be described as follows.

If the speed of the strip increases, for example,

the current generated by the tachometer generator 3| will increase thereby moving the core 33 downwardly against the force of spring 31. Lever 35 is thereby moved in a counter-clockwise direction to close exhaust valve 43 and open intake valve 4| of the pilot valve 38. The output pressure in line 44 is, therefore, increased, An increase in pressure in line 44 will act against diaphragm 41 of the chamber 46 in a manner described above in order to increase 'the output pressure in line 62. This pressure will act in a similar manner through relay 63 to increase the pressure in pipe 64. The increase in pressure applied through pipe 64 to valve 21 will cause this valve to open, thereby increasing the supply of fuel to the burners. Therefore, it will be seen that as the speed of the strip increases more heat will be supplied to the strip so that it can reach a given temperature in the shorter period of time required for a given length of the strip to move through the furnace. If the speed of the strip had decreased the relays 29, 45 and 63 would act in the opposite direction from that described to reduce the pressure applied to the diaphragm of valve 21. Therefore, this valve would close under the action of its spring to reduce the fuel supplied to the furnace.

Normally speaking, strip of a given weight or moving at a given speed will require a given amount of heat to bring it up to temperature as it is passing through the furnace chamber. If the speed of the strip is increased more fuel will be required to bring it to temperature in a given time. Likewise, if the thickness of the strip is increased more fuel will be required to bring it 6, to temperature at a given speed or the speed of the strip can be reduced as its thickness increases. The relation of speed and thickness to the temperature of the strip can be predetermined with a substantial amount of accuracy so that the generator 3! can operate to produce a given pressure for a given speed of strip. From time to time, however, due to substantial changes in speed of the strip or in thickness of the strip that is being handled it is necessary to vary the amount of fuel supplied to the furnace panels. This can be accomplished by an adjustment of relay 45 without in any way changing any of the rest of the apparatus. If, for example, the speed of the strip is to be increased, or the thickness of the strip at a given speed is to be increased it will be necessary to supply more fuel to the burners. This means that a larger air pressure must be applied to the diaphragm of valve 21 for a given output of generator 3|. This can be accomplished by shifting fulcrum 49 upwardly along lever 48. When the relay is in balance, movement of the pivot 49 upwardly will permit spring 53 to overcome the force of spring 5i and therefore cause valve 58 to open and increase the output pressure of the relay 45 for a given input pressure in chamber 46. A scale 59 is supplied for convenience in adjusting fulcrum 49 for given conditions.

In the normal operation of the system of the type disclosed herein minor variations in the thickness of the strip that occur as a result of normal rolling practice, for example, or variations in the B. t. u. content of the gas and similar variations that will occur from time to time, or a change in the temperature of the strip as it enters the furnac will cause the temperature of the strip leaving the furnace to vary slightly from its predetermined desired value regardless of the speed control. Means is provided in accordance with the present invention to adjust the heating effect of the furnace in accordance with the temperature of the strip since said temperature will reflect changes in the various uncontrolled variables that are mentioned above. To this end the temperature of the strip adjacent to the point at which it leaves the furnace is measured by a radiation pyrometer 13. This pyrometer is connected in the usual fashion with a control instrument 14 which is preferably an air control potentiometer. Air is supplied to this instrument through a line 15 under regulated pressure, and the pressure output from the instrument is varied in accordance with the temperature of the strip. This output is applied through a line 15 to a chamber H having as one wall thereof a movable diaphragm 69. Therefore, as the temperature of the strip varies the pressure in the chamber II will be varied to move pivot 55 of the relay 63. As shown, herein, the pivot is mounted on a carriage 66 which slides along a track 61'. The carriage is connected by a rod or link 68 to the diaphragm 69. Changes in position of the diaphragm are opposed by a suitably calibrated spring 12.

From the above it will be seen that changes in temperature of the strip will produce movement of the pivot 65 of relay 63 to thereby change the output pressure of this relay for a given pressure applied to the chamber 11. When the strip temperature is at the desired value, the output pressure of control instrument (4 will be such that diaphragm 69 holds pivot 55 at some predetermined point. If, for example, the temperature of the strip increases above its correct value" the control-instrument: 14 will produce. an increase ment of diaphragm 69 to the. leftagainst. the

force of spring 72. As this diaphragm. moves. it will move the pivot 65- to' the. left, thereby permitting the lever to tilt in a counter-clockwise direction under the force of the springs acting. thereon. This counter-clockwis movement will. cause the diaphragm of chamber 18 to move-away from: the exhaust valve of that chamber to reduce the pressureappliedthrough pipe 64 to the. control valve. Therefore, an increase in temperatureof the. stripwillcausea reductionin the fuel supply totheburners of the furnace.

From. the above description it will be: seen that there is provided a control system for a furnace in which the fuel is regulated in accordancewith the speed of the stripmoving. through the' furnace chamber. An adjustment of the instruments regulating the fuel supply can be made; in accordanc with the temperature of thestripso that ultimately the heating effect of the-furnace on the strip is controlled jointly by the speed with which it moves through the furnace as well as by its temperature. Means is also provided to adjust this system to compensate for diiferent.

speeds as well as fordifferent thicknessesof thestrip that are beyond normal adjustments that. can be accomplished rapidly by the average control system. While the system has been shown somewhat diagrammatically with respect to the control instruments used to accomplish the controlfunctions, it will be apparent to those skilledln the art that there are many control instruments that are commercially available which may be used' in a system of. the type. shown.

herein.

In Figure 4 there is shown a modified form. of control system. In. this system the fuel is regulated in accordance with the speed of the strip as in the system described in connection with Figure 3. This system differs from that of Figure 3,. however, in' that the temperatureof the strip is used tocontrol the-position of thepanels with respect to each other. When the panels. have moved to a predeterminedposition adjacent to or away from each other the regulator 63. is adjusted to vary the input-outputv pressure ratio sothat the fuel. supply will compensate for the new'panel position.

Referring, to Figure 4 it will be seen that the. radiation pyrometer l3 responsive to the strip temperature is connected toan electric control. potentiometer 8| of commercial type. This po-- tentiometer is used. to energize motor 9- in one direction or the other as-the temperature-ofthe strip deviates from its desired predetermined value. As shown, the panel 2 is provided witha switch actuating arm 83 that will operate limit switch 84 or limit switch85 depending upon the position of the panel. It. is intended that the limit switch 84 beoperated When'the panels have been moved to the position in which they are fully'closed as shown in Figure2 of the drawing. The switch 85 will be: operated when: the panels have been movedapart to such an extent that the seals it. are aboutto-be broken. Closing. of either switch 8A or 85 operates through. a-conventional interrupter mechanism 86 to energize motor '81 for operation in one direction or the other. The fulcrumfiS for the lever ofregulator 53 is moved in one direction or the other by .a' threaded shaft88 that is driven by motor 81.

In theoperation ofthis system-the speed of the. stripcontrolsthe pressure appliedto valve.2 li in 7;; pressure in line: 93,1Ts proportional to-the: speedofi 8 the: manner. described: in connection "with Figure- 3'. Asthe temperatureof the-stripvariesfrom its. desired value controller 8 I will operate'motor Eltomovethe panels toward or: away from each other.

, If. thetemperature of the strip increases motor 9 will. be energized for rotation in a direction to separate'the panels. Thismeans that the sources ofradiant heat-0n the surface of the panels will be: moved away from the strip so that it will be heated to a lesser degree for a given fuel supply-- and; therefore, the temperature of the strip will be. lowered. In like. manner, if the temperature: of the'strip is too: low, motor 8 will be energized for rotation in a direction to move the panels toward; the strip so that more heat can be placed? therein. When the panels have moved to one or. another of. their limits, indicating that further correction is required, one of. the limitswitches; will be operated to energizem'otor 87 tothereby rotateshaft 88. The shaft will be rotated in a. direction to produce anadjustment of the valve; pressurainlinei 64 which will increaseor decrease the supply of fuel depending. upon whether the panels are together or awayfrom each otherre-- -spectively. The pivot 65- of relay 63- will then:

remain inits. adjusted position until such time as one or the other of the limit switches is again operated. If, for example; the temperature has. decreased and the panels are moved to their limits toward each other, the switch: 84- will be.- operated: to energize motor 81 for rotation in a direction to shift fulcrum 65 of regulator 63 50 that the output pressure in line 6.4 will increase. The additional fuel supplied as a" result of this increased pressure will increase the temperature:

ofthe stripso that the panels may be movedzapart a. small distance. The panels will then floatv be-- tween the two limit positions unless somevariable. requires that they be moved suificiently to'actuate again one of the limit switches. The change intemperature of the panels can beeffectedrap idly so that itwouldbe possible to-overcorrect the. valve pressure if motor 31 was run continuously. 11110116. direction or the other untilthestrip actually reflected a change in. temperature as uneas ured by pyrometer 73. Therefore, an: interrupter 8B. isplaced in the line between the limitsw-itches- 84and85-and the-motor 8'1- so-that the motor. will be operated in steps of. a frequency determined by. the-setting; of the interrupter... This givesthe-sys tem a chance tostabilize at the new adjustment of regulator 63 before additional corrections are made to. this regulator.

Fromthe above/it willbe seen that-in this sys-i tern also, there is provided. control. of thefuel. in response. to. the speed of thestrip. Thereis also-a resetting or adjustment of the fuel supply in response to the temperature of. the strip. Thisadr justment of the fuel supply,.however, occurs in directly through the position of. the-panels-rather.

than directly from the strip temperature. as. was.

the case inFigureZ.

.InFigure5 there. isshown another embodimentof. theinvention in which the controlrofthe. stripheating isobtained byits speed: and temperature. In this embodiment of the invention, however, different control. instrumentalities are used.

Referring to the drawing; it-will be seenthat as the strip leaves the furnace it passes over a roller 91 which is driven thereby. This roller drives ahydraulic pump-92, the output side of which discharges into apressure line 93-. The pump is of a typethat the pressure produced will be proportional to the speedthereofsothat the the strip. This pressure is impressed upon a regulator 95 that is provided with a chamber having a movable diaphragm 91. The diaphragm is connected by a post 98 with a second diaphragm 99 having an opening therein which communicates with the atmosphere through an opening in the post. The diaphram 99 encloses a chamber I 9I that is supplied with air from a source under pressure at I02. Entrance of the air to the chamber II is regulated by an inlet valve I03 and exhaust from this chamber is regulated by an exhaust valve I04 that are normally biased toward their closed positions by a spring I 05. The pressure in chamber IOI is impressed upon the control valve 21 through a suitable pipe I 05. It will be seen that as the pressure in chamber 96 increases diaphragm 99 will be moved against valve I04 to close the exhaust port and open the inlet so that the pressure can increase in chamber IN and on the valve 21. This increase in pressure will be applied against diaphragm 99 to oppose the force of diaphragm 91 until the pressure produced in chamber IOI is proportional to the pressure in chamber 96.

The pressure of the pump in line 93 and chamber 96 can be relieved by a motor driven valve I08 inserted in a bypass line I01 leading to the intake of the pump. The valve I08 is energized for operation in an opening or closing direction to thereby vary the bleed through the bypass by means of a potentiometer controller I09 connected to the radiation pyrometer I3. The pressure in line 93 and chamber 99 can also be varied by a second bypass I I I that has a manually operated valve IIO therein. A suitable reservoir for the liquid used in the hydraulic system is provided at I I2.

In the operation of a system of this type, the pump 92 is driven in proportion to the speed of the strip and sets up a pressure proportional thereto. This pressure acts upon the regulator 95 to control the opening of valve 27. As explained above, the system is such that an increase in speed of the strip will increase the pressure on the diaphragm of valve 21 to open that valve and increase the supply of fuel. The manual valve I I in bypass III can be adjusted to vary the bleed through this valve and, therefore, the pressure in line 93 for a given strip speed as may be desired. This valve is intended to be adjusted in accordance with the normal speed of the strip or in accordance with its thickness so that the system can be stabilized for the normal operation thereof.

The temperature of the strip acting through potentiometer I09 and motor operated valve I08 is used to control the bleed through bypass I01 to thereby vary the pressure in the system for a given speed in accordance with the temperature of the strip. As the temperature of the strip increases valve I09 will be operated in a direction to increase the bleed through bypass line I01. This reduces the pressure applied in chamber 96 and consequently reduces the pressure of the air applied to the diaphragm of control valve 21. Thus, the speed of the strip controls the supply of fuel but this fuel is reset in accordance with the temperature of the strip.

Figure 6 uses substantially the same control system as that disclosed in Figure except that the temperature of the strip acts through potentiongieter I09 to adjust the heating panels I and 2 toward each other in a manner similar to that described above in connection with Figure 4. Heating panel 2 is provided with a switch oper-' ating member H5 that will actuate switch lit or switch I 11 depending upon whether the panels are moved to a predetermined position adjacent to or away from each other respectively. When the panels have moved to the limits of their travel and have operated switches the latter will close circuits to the motor operated valve I09 which circuits include therein an interrupter II8.

In the operation of this system the speed of the strip produces a pressure in line 93 proportional to the speed thereof. This pressure acts through regulator 95 to control the pressure applied to the diaphragm of valve 21. The temperature of the strip controls the position of the panels relative to the strip so that the heating effect hereof for a given supply of fuel can be varied in accordance with strip temperature. When the panels have moved to one or another of their limits and adjustment is made to the hydraulic system. This adjustment is such that if the panels have moved to their innermost positions, for example, the supply of fuel will be increased by an amount suflicient to cause the panels to open slightly. The temperature control will then cause the panels to float between their limit positions at this setting of the fuel valve until such time as conditions change to an extent requiring a readjustment of the valve I08 in the bypass line.

In Figures 5 and 6 there is shown a roller 9| over which the strip passes as it leaves the furnace. It will be obvious, however, that the pump 92 could be driven by the roller 4 as was the tachometer generator disclosed in Figures 3 and 4. It will also be obvious that the tachometer generator of Figures 3 and 4 could be driven by a roller placed beyond the exit of the furnaces in the manner of roller 9| if it was so desired.

In the manufacture of tin plate stock, for example, it is customary to use cold rolled and annealed low carbon strip from 0.008 to 0.010 inch in thickness. The strip is first passed through an electrolytic tinning bath and then through a furnace to fuse the tin coating. The fusing process must be carefully controlled to heat the strip slightly above the melting point of tin so that it will flow into a bright, smooth coat, but not high enough to affect the metallurgical characteristics of the base metal. This process is accomplished at high speed in a highly satisfactory manner with the apparatus of the present invention.

Electrolytically tinned strip of 0.0088 inch thickness is passed at the rate of 600 feet per minute in a vertical direction between the heating panels. Suitable apparatus is provided to attach the trailing end of one coil of strip to the leading end of the next so that the process may be continuous.v The furnace used to heat the strip comprises a pair of panels each 12 feet 9 inches long. The panels are designed so that, in their closed position the burner faces are 7.5 inches from the strip. Each panel can have a movement of 2.5 inches during the operation of the system, and normally the panels are in ap proximately their mid-position, or with the burners from 8 to 10 inches from the strip. When the furnace is fired at a pressure of 25.5 inches water column with a combustible mixture of city gas and air the furnace chamber will be heated to 1950 F. Travelling at the rate of 600 feet per minute the strip will be in the furnace about 1.25 seconds, and during that time will be brought up to 475 F. Since the melting point of tin is 450" F., the tin will flow into a smooth, shiny coat that freezes almost immediately upon leaving: the furnace chamber.

Ordinarily the thickness of the strip andthe speed that it is to be moved through the furnace for a given run are determined before the run starts. The relay 45 of Figures 3 and 4 or the valve H of Figures 5 and 6 is set for these conditions. Thereafter, ordinary variations in the speed of the strip, and consequently its temperature, will be compensated for rapidly by the control system so that the temperature of the strip as it leaves the furnace will remain substantially constant. In systems of the type disclosed herein the strip temperature can be maintained at the desired value over a wide range of speed variation by varying the supply of fuel. It has been found that the efiiciency of the system increases with an increase in strip speed.

While the present invention is particularly applicable to control the heating of strip metal in the process of annealing or tin fusion it is equally as applicable to control the heat of any other web. Such an application may be, for example, the drying of ink on a printed web or the drying of paper as it is passing through a paper-making machine. In any event, the control of the heating is responsive to the speed of the strip and this control is supervised by the temperature of the strip. lhe supervision can be such that it acts directly upon the fuel control valve or it can act upon this valve indirectly through the position of the heating panels.

While in accordance with the provisions of the statutes, I have illustrated and described the best form of embodiment of my invention now known to me it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit and scopeof the invention, as set forth in the appended claims, and that in some cases certain features of my invention may be used to advantages without a corresponding use of other features.

What is claimed is:

1. Apparatus for heating continuously a strip of sheet material comprising an elongated furnace having a chamber through which the strip passes, heating elements in said chamber to heat said strip, means through which fuel is supplied to said heating elements, regulating means to adjust the supply of fuel, means responsive to the speed of the strip having a part thereof movable as strip speed varies, means responsive to the temperature of said strip having a part thereof movable as strip temperatures varies, and mechanism .to adjust said regulating means said mechanism including elements moved by said parts, and means adjusted jointly by said elements.

2. Apparatus for heating continuously a strip of flexible material comprising structure forming an elongated furnace chamber through which the strip passes to be heated, heating elements in said chamber to heat the strip, means through which fuel is supplied to said heating elements, valve means to regulate the flow .of fuel, means operative to produce responses varying in accordance with the speed of the strip through said furnace having a part thereof movable as strip speed varies, means operative to produce responses in accordance with the temperature of the strip as it leaves said furnace chamber having a part thereof movable as strip temperature varies, andmechanism to regulate said valve said mechanism including elements moved by said parts, and means adjusted jointly by iidi 4 16- ments.

3. Apparatus for heating continuously sheet material passing in a stripfrom a point of "supply to a point of use comprising structure forming a furnace having a chamber therein through which the strip travels, a plurality of heating elements in said chamber, means through which fuel is supplied to said elements, aregulating device for saidfuel, speed responsive means operative :to produce responses proportional to the speed of the strip as it passesthrough said cham ber, mechanism operated by said responses to adjust said regulating device, temperature responsive means operative to produce responses proportional to the temperature of the strip-and means forming a portion of said mechanism :operated by the responses of said temperature responsive means to vary the adjustments thereof for a given response of said speed responsive means.

4. Apparatus for heating continuously a strip of material comprising structure forming a furnace chamber through which the strip travels, a plurality of burners in said structure to heat said chamber, a fuel supply line for saidburners, valve means in said fuel line to regulate the fiow of fuel, means responsive to the speed of the strip moving through said chamber, mechanism operated by the responses of said speed responsive means to adjust said valve means,said mechanism including adjustable parts therein operative to vary the adjustment of said valve means for a given speed of said strip, temperature responsive means mounted to respond to the temperature of said strip as it leaves said chamber, and means operated by said temperature responsive means to adjust the parts of said mechanism.

5. Apparatus for heating continuously strip material comprising structure "forming a furnace having achamber through which the strip passes, burners in said structure to heat said chamber, a fuel line to supply fuel to said burners, a valve in said line to regulate the supply of fuel, means responsive to the speed of the strip as it moves through thefurnace, mechanism operated by the responses of said speed responsive means to adjust said valve, means to transmit responses of said speed responsive means to said mechanism and including regulating means to vary the response delivered to said mechanism for a given speed, temperature responsive means to respond to the temperature of said strip as it leaves said furnace, and means operated by said last-mentioned means to adjust said mechanism, whereby said mechanism will be-adjusted in accordance with the speed'and temperature 0 said strip.

16. Apparatus for heating continuously strip material including structure forming a furnace including a pair of opposed panels, i'side "membersto 'close the space between the'edgesio'f said panels to form a furnace chamber, means mounting said panels for movement toward and from each other, means to move said panels, va :plurality of burners in said panels to supply heat to the strip, conduit means to conduct fuel to said burners, a valve in said conduit means, means responsive tothe speed of the-strip,-.mechanism operated by said responsive means to adjust said valve and vary the supply of fuel to said burners, means responsive ,to the temperature of the strip, .and mechanism operated by said temperature responsive means toadjust said moving means to vary the distance between said panels and .said-strip'i thereby phangeithe heat- 13 ing effect of the burners for a given adjustment of said valve.

7. The combination of claim 6 including a pair of switches, one of which is mounted adjacent to each end of the path of movement of one panel, means movable with said one panel to actuate a switch when said panel reaches one or the other of two predetermined positions, and mechanism operated in response to the actuation of one switch to adjust said valve in one direction and in response to the actuation of the other switch to adjust said valve in the opposit direction.

8. The combination of claim 7 including means to render the operation of said mechanism intermittent.

9. The combination of claim 6 including an operating part movable with one of said panels, a first means located to be engaged by said part at the limit of its movement in one direction, a second means located to be engaged by said part at the limit of its movement in the opposite direction, additional mechanism to adjust said valve, and means to operate said additional mechanism in one direction by engagement of said first means by said part and in the opposite direction upon engagement of said second means by said part.

10. The combination of claim 9 including means to render the operation of said additional mechanism intermittent.

11. Apparatus for heating continuously a strip of material comprising a furnace including a pair of oppositely disposed panels, means to move said panels toward and from each other to vary the distance between them and the strip, a plurality of burners in each panel, means to supply fuel to said burners including an adjustable valve, means responsive to the speed of the strip passing through said furnace, mechanism operated by said speed responsive means to adjust said valve in an opening direction upon increase in speed and in a closing direction upon a decrease in speed, means responsive to the temperature of the strip as it leaves said furnace, mechanism operated by said temperature responsive means to adjust said moving means to move the panels toward each other upon a decrease in strip temperature and away from each other upon an increase in strip temperature to thereby vary the heating effect of said burners on said strip for any given adjustment of said valve.

12. A paratus for heating continuously a strip of material comprising structure forming a furnace having a pair of oppositely disposed panels between which the strip moves, a plurality of heating elements in each of said panels and facing said strip, means to supply fuel to each of said elements, valve means to control the supply of fuel, a hydraulic pump, means forming a closed fluid circuit between the outlet and inlet of said pump, means driven by said strip in proportion to the speed thereof to drive said pump whereby a pressure proportional to strip speed is impressed in said circuit, means responsive to the pressure in said circuit to operate said valve means, an adjustable restriction in said circuit, means responsive to the temperature of said strip, and means to adjust said restriction operated by said temperature responsive means.

13. The combination of claim 12 including a by-pass in said circuit around said pressure responsive means, and means to vary the flow of fluid through said by-pass.

14. Apparatus for heating continuously strip material comprising structure forming a furnace having a pair of oppositely disposed and movable panels between which the strip moves, a plurality of heating elements in each of said panels, means to supply fuel to each of said elements, valve means to control the supply of fuel, means to move said panels toward and from each other to vary the heating effect of said elements on said strip, a hydraulic pump, means forming a closed fluid circuit between the outlet and inlet of said pump, means responsive to the pressure in said circuit, means operated by said pressure responsive means to adjust said valve means, means driven by said strip in proportion to the speed thereof to operate said pump whereby said valve means will be adjusted in accordance with strip speed, means responsive to the temperature of said strip as it leaves said furnace, mechanism operated by said temperature responsive means to actuate said moving means in accordance with strip temperature, a variable restriction in said fluid circuit, and mechanism operated by one of said panels as it moves to a predetermined position to adjust said variable restriction.

15. Apparatus for heating continuously strip material comprising a pair of oppositely disposed heating panels forming a furnace chamber between which the strip is moved, a plurality of radiant type burners in each panel facing the strip, means including a control valve through which fuel is supplied to said burners whereby the burners may be heated to supply radiant heat to the strip to raise the temperature of the same, means responsive to the speed of said strip operable to adjust said control valve and vary the supply of fuel to said burners, and means responsive to the temperature of the strip as it leaves said chamber to vary the radiant heat placed in said strip.

16. The method of controlling the heating of a strip of material moving continuously through a heating zone which comprises supplying fuel to said heating zone to be burned therein, heating the strip as a result of the burning fuel, measuring the speed of the strip as it passes through said heating zone and setting u impulses proportional thereto, utilizing said impulses to regulate the supply of fuel in accordance with the speed of the strip, measuring the temperature of the strip as it leaves said heating zone and setting up impulses proportional thereto, and using said impulses to control the amount of fuel supplied for a given strip speed.

KARL L. DIETRICH.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,386,645 Moore Aug. 9, 1921 1,971,666 Webster Aug. 28, 1934 2,089,015 Bucknam et al Aug. 3, 1937 2,143,672 Archibald Jan. 10, 1939 

